1) Lacs 
(also See Parabens, Formaldehyde, Imidazolidinyl Urea) Leading cause of contact dermatitis. Less irritating and allergenic preservatives include grapefruit-seed extract, phenoxyethanol, potassium sorbate, sorbic acid, tocopherol (vitamin E), Vitamin A (retinyl) and Vitamin C (ascorbic acid).
Substances capable of slowing down or preventing the reactions of decay.
Compounds that are added to multi-dose vaccine vials to prevent bacterial and fungal growth. The most commonly used product is called thiomersal, a mercury-containing compound.